The IL-4 promoter contains multiple Stat6 binding sites. (A) The ability of recombinant Stat6 to bind oligonucleotides containing the human P elements was determined by EMSA. Stat6 bound the P1, P2, and P4 probes (solid arrow). An additional slowly migrating complex (open arrow) formed on the P1 oligonucleotide (and occasionally on the P2 probe; see Fig 8). The relative migration of the free probes, which were of similar length (see Materials and Methods) and radiolabeled with similar specific activity, is not shown in this figure. (B) Alignment of the P elements that supported Stat6 binding with the composite C/EBP-Stat6 site from the germline IgE promoter. The P2 oligonucleotide is shown in opposite orientation than in Fig 2. Binding sites for NFAT, Stat6, and C/EBP are indicated by boxes. C/EBP proteins may interact with the P0, P1, and P4 NFAT elements, although the precise nucleotide binding sites have been reported only for the P4 sequence.36